Turbines are used in a variety of applications, such as aircraft engines, rocket engines, and other applications. Many of these applications expose the rotating turbine blades and stationary vanes (hereinafter referred to collectively as blades) of the turbine to extreme heat or cause the turbine blades to become extremely hot. This heat is dissipated using a cooling system that delivers cooling fluids to the turbine blades through complex interior cavity systems in the turbine blades. The cooling fluids enter the turbine blades through the end of the turbine blade coupled to the turbine housing and escapes through cooling holes in the blades (not shown).
Turbine blades are typically manufactured using a casting process. The complex interior cavity systems that form part of the cooling system are formed using core blocks. The core blocks have support projections that form apertures after the casting process. Often, these support projections are affixed to the mold at the end of the mold that forms the closed end of the turbine blade, which is also commonly referred to as the tip shelf of the turbine blade. Thus, once a turbine blade has been cast, and the mold and core block have been removed, the resulting turbine blade contains holes, or apertures, where the support projections where located during formation of the turbine blade. It is necessary to plug these holes formed by the support projections for the turbine blade to operate safely and for the turbine blades to realize the maximum cooling efficiencies offered by the cooling system. Otherwise, the cooling system cannot operate as designed, which may result in catastrophic damage to the turbine blades and other turbine components upon failure of the turbine blade.
Sealing these holes made in the turbine blades during the manufacturing process has been addressed in many ways in the past. For instance, the holes were closed using, for instance, brazing and fusion welding processes. However, high temperature superalloys, which are commonly used to form turbine blades, can be difficult to weld. In addition, brazing superalloys typically requires additional preparation and tighter fit up to produce a quality joint. More importantly, brazing often results in inferior joints due to defects and the brittle nature of the bond. Fusion welding often results in cracking of the weld metal and base metal affected by the weld. Thus, the use of brazing or fusion welding has not always produced reliable results.
In another example, the diameter of the support projections are reduced to very small bores. However, this solution increases the complexity of the manufacturing process by restricting the allowable tolerances and, therefore, increasing the cost of producing turbine blades.
Yet another solution for closing holes in the tip shelf of a turbine blade is described in U.S. Pat. No. 6,193,468 to Beeck et al. and shown in FIG. 1. Beeck discloses sealing an aperture in a tip shelf by inserting a closure member into another aperture that orthogonally intersects the aperture in the tip shelf. The method disclosed in Beeck requires that another hole be drilled in the turbine blade, which can further weaken the turbine blade and interfere with the structural integrity of the turbine blade.
Thus, a need exists for a simplistic and reliable system for sealing apertures formed in the outer wall of turbine blade bodies during manufacture of turbine blades.